Here's an answer from some time back......5 '96

Groovy
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Bob Holmes said....

The TCE of FR-4 is non-isotropic and it varies with resin content and
temperature.  Resin has a much higher TCE than glass, so in-plane TCE is
severely restrained by glass.  Out-of-plane, the glass provides little
restrain
and the TCE can be 50 ppm/C or higher. In the plane of the glass cloth, low
resin materials such as the FR-4 used for DSR can have a TCE as low as 14 or
15
ppm/C. The higher resin content cores used in an MLB can have an in-plane
TCE
as high as 20 ppm/C.  As an approximation I usually use 17ppm/C as an
average
in-plane value.  This matches copper and if a PWB contains a lot of copper
it
will tend to move the TCE toward this value.

Near Tg, the in-plane TCE begins to rise until the material reaches a
temperature slightly above Tg.  At that point, the modulus of the resin
drops
dramatically and the glass cloth begins to dominate.  This increases the
out-of-plane TCE and reduces the in-plane TCE.  Values of in-plane CTE in
the
range of 10 ppm/C can be observed at this point.

Robert R Holmes PhD
Lucent Technologies (formerly AT&T)
[log in to unmask]

-----Original Message-----
From: John Brewer [mailto:[log in to unmask]]
Sent: Tuesday, October 05, 1999 10:17 AM
To: [log in to unmask]
Subject: [TN] FR-4 Coeff of thermal expansion? Material Data?


Can anyone point me to

(specifically) coeff of thermal expansions for FR4
(generally) material properties for same?

Thanks!
John

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